Three cases of osteosarcoma (stage IIB) of the proximal fibula were successfully treated by marginal excision that preserved the common peroneal nerve and lateral stabilizers of the knee joint. Caffeine-assisted chemotherapy was administered to three boys, ages 15, 17, and 11 years, and resulted in a complete response. Two patients initially presented with peroneal nerve palsy that resolved completely with preoperative chemotherapy. The subsequent intentional marginal procedures resulted in preservation of the common peroneal nerves, lateral collateral ligaments, and biceps femoris tendons. In two cases the collateral ligament and biceps tendon were reattached to the tibia with a spike washer or suture anchors, and in the third case they were reattached by suture only to the ligamentous and capsular structure of the tibia. All three patients have normal ankle and knee joint function without evidence of recurrence 122, 120, and 61 months after surgery, respectively. Preservation of limb function without compromising the principles of tumor surgery is a desirable goal in any patient but particularly in young patients. For patients with osteosarcoma of the proximal fibula, this approach provides a better quality of life than conventional wide excision.